The present invention relates to an internal combustion engine with two cylinder banks each having a valve operating device enabling valve timing and valve lift characteristic to be varied, and in particular being capable of changing both valve timing and valve lift characteristic (working angle and valve lift) of intake and/or exhaust valves depending on engine operating conditions, and specifically to a variable valve timing and variable valve lift characteristic device applicable to a two-bank engine in which a cylinder head and intake and exhaust valves arranged in one cylinder bank and a cylinder head and intake and exhaust valves arranged in the other cylinder bank are substantially mirror-symmetrical with respect to a centerline of the two cylinder banks.
In recent years, there have been proposed and developed various types of variable valve timing and valve lift characteristic mechanism which variably adjust both valve timing and valve lift characteristic (working angle and valve lift) of intake and/or exhaust valves, for the purpose of improved fuel economy (low fuel consumption) and enhanced stability (stable engine operations) at low-speed light-load operation, and sufficient engine power output resulting from the enhanced charging efficiency of intake air at high-speed heavy-load operation. One such variable valve timing and variable valve lift characteristic mechanism or device has been disclosed in Japanese Patent Provisional Publication No. 55-137305 (hereinafter is referred to as JP55-137305). The variable valve timing and variable valve lift characteristic mechanism or device as disclosed in JP55-137305, includes a drive shaft rotating in synchronism with rotation of an engine crankshaft, a camshaft having cams and fitted on the outer periphery of the drive shaft to be relatively rotatable about the drive shaft, a rockable cam provided on the outer periphery of a support shaft for driving intake and exhaust valves, an eccentric cam provided eccentrically on a control shaft, and a rocker arm rotatably fitted onto the outer periphery of the eccentric cam for mechanically linking the associated cam with the rockable cam therethrough. Rotating the control shaft varies the center of oscillating motion of the rocker arm, thereby varying a valve lift characteristic of intake and/or exhaust valves.
Assuming that the variable valve timing and variable valve lift characteristic mechanism or device as disclosed in JP55-137305 is applied simply to each of two cylinder banks of a V-type engine without full deliberation upon the layout of the variable valve timing and variable valve lift characteristic mechanism or device with regard to a direction of rotation of each of the drive shafts, there is a possibility that valve lift characteristics of left and right banks differ from each other.
Accordingly, it is an object of the invention to provide an internal combustion engine with two cylinder banks each having a valve operating device enabling variations of valve timing and valve lift characteristic (working angle and valve lift), which avoids the aforementioned disadvantages.
It is another object of the invention to provide a valve operating device for an internal combustion engine with two cylinder banks each having a variable valve timing and variable valve lift characteristic mechanism in which a valve lift characteristic of a first bank of the two cylinder banks is essentially equivalent to that of the second bank during variable valve-lift control.
In order to accomplish the aforementioned and other objects of the present invention, an internal combustion engine with a crankshaft and two cylinder banks, each cylinder bank having a cylinder head and a valve operating device enabling both valve timing and valve lift characteristic to be varied, each valve operating device comprises a drive shaft installed in the cylinder head of each cylinder bank and rotating in synchronism with rotation of the crankshaft, the drive shaft having a center and an axis of rotation, an eccentric cam fixedly connected to the drive shaft so that a center of the eccentric cam is eccentric with respect to the center of the drive shaft, a rockable cam arranged to drive at least one engine valve, a power-transmission mechanism mechanically linking the eccentric cam to the rockable cam, a control mechanism provided for varying an attitude of the power-transmission mechanism, and as viewed in the same axial direction, a lifting direction of the rockable cam arranged in a first one of the two cylinder banks relative to a rotational direction of the drive shaft arranged in the first cylinder bank, and a lifting direction of the rockable cam arranged in the second cylinder bank relative to a rotational direction of the drive shaft arranged in the second cylinder bank are set to be identical to each other.
According to another aspect of the invention, an internal combustion engine with a crankshaft and two cylinder banks, each cylinder bank having a cylinder head and a valve operating device enabling both valve timing and valve lift characteristic to be varied, each valve operating device comprises a drive shaft installed in the cylinder head of each cylinder bank and rotating in synchronism with rotation of the crankshaft, the drive shaft having a center and an axis of rotation, a control shaft extending substantially parallel to the drive shaft and rotated toward and held at an angular position based on engine operating conditions, a rockable cam fitted to an outer periphery of the drive shaft so as to be relatively rotatable about the drive shaft and to drive at least one engine valve, an eccentric cam fixedly connected to the drive shaft so that a center of the eccentric cam is eccentric with respect to the center of the drive shaft, a first link member fitted to an outer periphery of the eccentric cam so as to be relatively rotatable about the eccentric cam, a control cam fixedly connected to the control shaft so that a center of the control cam is eccentric with respect to a center of the control shaft, a rocker arm whose one end is linked to a tip end of the first link member so as to be rotatable relative to the first link member, the rocker arm being fitted to an outer periphery of the control cam so as to be relatively rotatable about the control cam, a second link member linked to both the other end of the rocker arm and the rockable cam so as to be rotatable relative to both the rocker arm and the rockable cam, as viewed in the same axial direction and when using a valve stem axis of the engine valve as a reference, the valve operating device arranged in the first cylinder bank and the valve operating device arranged in the second cylinder bank are laid out substantially similarly to each other, and the rotational direction of the drive shaft arranged in the first cylinder bank and the rotational direction of the drive shaft arranged in the second cylinder bank are set to be identical to each other.
According to a further aspect of the invention, a valve operating device for a V-type internal combustion engine equipped with a crankshaft and left and right cylinder banks, each cylinder bank having a cylinder head and a variable valve timing and variable valve lift characteristic mechanism, comprises a drive shaft installed in the cylinder head of each cylinder bank and rotating in synchronism with rotation of the crankshaft, the drive shaft having a center and an axis of rotation, an eccentric cam fixedly connected to the drive shaft so that a center of the eccentric cam is eccentric with respect to the center of the drive shaft, a rockable cam arranged to drive at least one engine valve, a power-transmission mechanism mechanically linking the eccentric cam to the rockable cam, a control mechanism provided for varying an attitude of the power-transmission mechanism, and as viewed in the same axial direction, a lifting direction of the rockable cam arranged in a first one of the left and right cylinder banks relative to a rotational direction of the drive shaft arranged in the first cylinder bank, and a lifting direction of the rockable cam arranged in the second cylinder bank relative to a rotational direction of the drive shaft arranged in the second cylinder bank are set to be identical to each other, the lifting direction being defined as a direction of oscillating motion of the rockable cam from a position that the engine valve begins to lift to a position that the engine valve reaches a maximum valve-lift state in which a magnitude of valve lift of the engine valve is a maximum value.
According to a still further aspect of the invention, a valve operating device for a V-type internal combustion engine equipped with a crankshaft and two cylinder banks, each cylinder bank having a cylinder head and a variable valve timing and variable valve lift characteristic mechanism, comprises a drive shaft installed in the cylinder head of each cylinder bank and rotating in synchronism with rotation of the crankshaft, the drive shaft having a center and an axis of rotation, a control shaft extending substantially parallel to the drive shaft and rotated toward and held at an angular position based on engine operating conditions, a rockable cam fitted to an outer periphery of the drive shaft so as to be relatively rotatable about the drive shaft and to drive at least one intake valve, an eccentric cam fixedly connected to the drive shaft so that a center of the eccentric cam is eccentric with respect to the center of the drive shaft, a first link member fitted to an outer periphery of the eccentric cam so as to be relatively rotatable about the eccentric cam, a control cam fixedly connected to the control shaft so that a center of the control cam is eccentric with respect to a center of the control shaft, a rocker arm whose one end is linked to a tip end of the first link member so as to be rotatable relative to the first link member, the rocker arm being fitted to an outer periphery of the control cam so as to be relatively rotatable about the control cam, a second link member linked to both the other end of the rocker arm and the rockable cam so as to be rotatable relative to both the rocker arm and the rockable cam, as viewed in the same axial direction and when using a valve stem axis of the intake valve as a reference, the valve operating device arranged in the first cylinder bank and the valve operating device arranged in the second cylinder bank are laid out substantially congruently with each other, and the rotational direction of the drive shaft arranged in the first cylinder bank and the rotational direction of the drive shaft arranged in the second cylinder bank are set to be identical to each other.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.